Radio beacon



Dec. 30, 1947. I c, w. EAR-P 2,433,351

RADIO BEACON l v Filed Aug. 1l, 1943 2 Sheets-Sheet l INSTRUME/Vf Recs/v5@ V2 AMPL/F/sn berscvnm ,a s/a/a L OMN/ o/PRr/ONAL A TO PHASE Inventorv CHARLES WILL/AM EA Q Dec, so, 1941. 1w-EMP 2,433,351

RADIO BEACON Filed Aug. 1l, 1943 2 Sheets-Sheet 2 OMN/ D/PECWONA L of/ I f FREQUENCY GEA/52A To@ Monahan@ PHASE SH/rse FREQUENCY Fl GENERATOR MODULArp/z OZ/rPuroFD of] fl MA Ll Patented Dec. 30, 1.947

RADIO BEACON Charles William Earp, London, England, assignor, by mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application August 11, 1943, Serial No. 498,197

In Great Britain February 23, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires February 23, 1960 (Cl. Z50-11) 16 claims. 1

The present invention relates to a two-tone radio beacon, the true geographic bearing of which can be obtained on a mobile vehicle on a directly reading indicator. In a known system, two separate transmissions are necessary, and two receivers are required on the vehicle. It is the object of the present invention to provide a twotone beacon which requires one transmission carrier wave only, and one receiver.

In the known system, a carrier wave is applied to an omni-directional aerial, and is modulated also by two tones of frequencies f1 and f2 in separate modulators, the outputs from which are applied to two directive aerials. A comparison of the relative levels of the two modulations (both in amplitude and sense of phase) at the mobile receiver gives a direct indication of the bearing. It is necessary, however, to radiate a comparison transmission in which the two tones are sent out omni-directionally, and this necessitated a second carrier frequency to be used. According to the present invention two auxiliary tones are radiated omni-directionally as sidebands of the original carrier wave, and the comparison tones are derived from these two auxiliary tones.

The invention will be better understood from the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 shows diagrammatically the circuit arrangements cf the transmitter according to the invention.

Figs.12a, and 2b show diagrammatically circuit arrangements of two receivers for working in conjunction with the transmitter shown in Fig. 1;

, Fig. 3 shows the arrangement of Fig. 1 modified for the case in which f1=fa but a phase displacement is given to one of the modulating cornponents, hence producing in effect a rotating beacon;

Fig. 4 shows a modied form of receiver for use in conjunction with the transmission system of Fig. 3; l

Fig. 5 shows diagrammatically the circuit arrangements of a transmitter of another embodiment of the invention; and

Fig. 6 shows the circuit arrangements for a receiver for use in conjunction with theV transmitter shown in Fig. 5.

Referring to Fig. l', the carrier frequency F from generator CO is modulated in modulator M by both low frequencies f1 and f2 generated in oscillators Ofi and Ofz and represented respectively by er sin Zrr fit and e2 sin 21rf2t, the.

output from modulator M, containing both carrier and sidebands being applied to an omni-directional aerial VI.

The two low frequencies f1 and f2 from oscillators Ofi and Ofz are also combined in a modulator D to give .two derived frequencies (f1-fz) and (f1-H2) which are filtered from each other in filters FI and F2 before each is applied with carrier frequency wave to modulators MA and MB respectively. The outputs from MA and MB, each composed of tWo sidebands, are applied to two directional aerial systems LI` and L2 which .each have figure of eight directive characteristics arranged perpendicularly to each other.

Figs. 2a and 2b show suitable receivers for the beacon transmission of Fig. 1. Figs. 2a and 2b are so similar that Fig. 2a only will be explained in detail. The modulated waves are received on a single omni-directional antenna V2 and are amplied in amplier A from which the output is applied to a detector D from which the four modulation frequencies f1, f2, fi-fz and fi-l-fz are produced. Frequencies fr and f2 are selected by filters FRI and FB2 respectively and passed to a modulator MR.v which produces two derived frequencies fi-fz and fi-l-fz. These derived frequencies are ltered by filters FSI and FSZ respectively and applied to the field coils Y, X of the indicator B respectively.

The frequencies f1-f2 and fi-l-fz produced in the detector D are filtered out by lter FSS and applied to the third windings S of the indicator B.

The amplitude of the received frequency fi-fz will depend on the position of the receiver with respect to the field pattern of the antenna Ll and the amplitude of the received frequency fi-l-fz will depend on the position of the receiver with respect to the field pattern of the antenna L2. Voltages at these two frequencies and at the relative values depending on the position of the receiver are delivered by the filter FS3 to the deflected member S of the indicator B. The windings X and Y at right angles to each other are supplied by the derived frequencies fi-fz and ,fi-I-fz from the modulator MR. These frequencies have equal amplitude, since they are derived from the modulation on the omni-directional antenna VI. The result is that the deflected member S will assume a rotational position with respect to the deecting members X and Y which will be determined by the relative amplitudes of the frequencies in the winding S. y

Alternatively, as shown in Fig. 2b the derived `frequencies (ji-kfz) and (fi-42) may be applied to the winding S of the indicator B, and the sum frequency (f1-H2) applied to one stationary WindingXand thedilerence frequency (f1-f2) to the Yother :stationary windingY. Herethe relative amplitudes of the frequencies in the windings X and Y will depend on the position of the receiver with respect to the field patterns of antennas LI and L2 While the derivedfre- 21rFt, the total omni-directional transmission can be represented by: E sin 21rFt+e1 sin 21rFt sin 21rf1t-l-e2 sin 21rFt sin 21rf2t The directional transmissions are:

R sin'21rFt sin'21r(f1*f2)t from MA and Li and R sin 21r Ft sin 21r(f1|f2)t from, MB and L2 in Which'R is .a constantfdepending Xupon E, e1 and ez.

At the/receiver which is ina directionfmaking an angle 0 with the direction of zero transmise sion from the directional 4aerial Ll fed by -MA the received signal-is proportional to:

On detection in the receiver of Fig. 2a,the outp ut will contain componentsat frequencies f1, fz,

'fr-fafii-fz in the following proportions:

'fly el f2; '-'62 ff 1**"f2, R [Sin-0 fafa 'Rsi The components fir-f2 andfr-Hz are -applied tothe moving coil -ofla dynamometer type indicator, which ta-kes up an angle p with one 'eld coil.

The components f1 and j2are applied to the modulator MR which delivers two components VWhich are or are'arranged' to be of equal intensity :'atifi-fz) and (f1-H2) toithei'ield coils'Y and X.

For equilibrium of the indicator:

latine frequency and the invention may beY erf i.plied to such system.

This modification of-Fig. flgis qshown. in. Fig, 3, Where f1 and f2 .i of Fig. lihave bothbecome f,

scarrier. frequency@ andfrequency -z @recombined aerial .of the transmit- 4. in M, and the non-directional radiation from Vi can be represented by:

sin 21r Fi-te SIIZ'IT 'Ff2;'S.l1L2/rj'ft Where the Wave of frequency 'f is represented by The low frequency wave of frequency f is also doubled in frequency in harmonic generator HG, and the double frequency 2f is split into diphase `current before-application to the modulators MA and MB. For this purpose a portion of the output from harmonic generator HG is applied directly to modulator MA and another portion lis passed to a`90 degree phase shifter PS before application to'modulator MB.

The directional radiation can be represented by:

Rrsin 21- Ft sin 4W ft from MA, `or LI and VR1 being the amplitude vof the Wave.

Fig. 4 shows the lmodified 'form of receiver which is used WithV the transmission system shown in Fig. 3. The Waves received from omni-directional antenna V2 are 'amplified in amplier A and detected in detector D in the output of which are the frequencies f and 2f. These frequencies are filtered out separately vbyz-i-llters Ff and F2f and the frequency f is doubled in harmonic generator HGR andthe outputsfat iA and B from harmonic generator HGR andlterFZf are applied to a suitable phase diiferenceindicator.

In the distancefat an angle 0 from the direction of zero transmission from antenna LI, the total signal picked up bythe yreceiver shown in Fg. 4 is proportional to:

Rlsin armeni (41rf+g)-sin (a+-275) The low frequency output vfrom vdetector D contains components of f and'Zfandrthisvlatter can be represented by:

Where K is a constant depending upon E, eand R1. The output from harmonic generator HGR is Where K1 is a constant.

AThe outputs at A and B, of frequency 2f, therefore diier in phase by (1i-*0), so that ay phasev meteractuated Vby them, can be arranged to give A suitable receiver is depicted in Fig, 6, the outputs from A and B being applied to a phase difference indicating meter. It is considered that these two figures are self-explanatory after the foregoing description and that no detailed description is necessary.

In all the systems described hereinbefore, there is a possible source of error in the receiving equipment, namely, the generation of tones in the low frequency detector in incorrect proportions, due to non-linearity of detection. In Fig. 2a for example, the output of detector D may contain frequencies (f1-f2) and (f1-H2) due, not only to the modulation of the directive signals, but to the modulation frequencies f1 and f2. Such an effect will, of course, be minimised by careful design of apparatus, and also by the use of less intense modulation by f1 and f2 than by (f1-fz) and (f1-Hz).

A still further refinement is provided by the use of a different relationship between modulation frequencies for the directive and comparison or omni-directional sidebands. For example, if f1 and f2 are used to modulate the omni-directional carrier F, then the frequencies 2(11-12) and 2(11-1-12) may be derived for modulation of the directive radiations, by first generating the harmonics 2f1 and 212, then beating together to produce 2(;f1f2) and 2(;f11f2) The receiver would be modifled in a similar manner, the low frequencies 2(fif2) and 2(11-1-32) being both applied to the deflected member of the indicator, and the equal amplitudes of 2(f1-f2) and 2(f1+fz) for the deiiecting members being derived from f1 and f2 as in the transmitter.

Though in the description hereinbefore given -the carrier wave has been modulated by low frequencies, the scope of the invention is not confined to the use of valve modulators.

In order to maintain the high degree of balance between the modulators MA and MB of Fig. 1 without the use of automatic correction circuits, so that the field pattern radiated does not vary, it is possible to use the mechanical form of modulator. Applied to the system of Fig. 1, four mechanical modulators would be used, geared together for relative speeds of rotation of f1, f2, f1-f2, and fia-fz.

The system should preferably use double sidebands for each modulation, as in this case there is less likely to be phase distortion of the low frequency waves produced in the receiver. The scope of the invention is, however, not confined to the use of double sideband transmissions.

As in the known arrangements the omni-directional carrier may be modulated by speech or other intelligence, simultaneously with the normal navigation service.

What is claimed is:

1. A radio beacon system for obtaining directly on a mobile receiver the angular position with respect to the transmitting station comprising means to generate a single radio frequency carrier wave, means to generate a plurality of low frequency waves, means to modulate the single radio frequency carrier wave by a pair of low frequency waves, means for radiating omni-directionally at least one of the sidebands correspending to the pair of waves, means for modulating the carrier frequency with two waves from at least one other low frequency wave, an angularly related directive aerial system and means connecting one modulator of the other low frequency wave to one directive aerial and the other 6 modulator to another directive aerial for radiating the sidebands corresponding to the other of the low frequency waves.

2. A radio beacon system as claimed in claim l comprising at a receiver means for obtaining the sideband frequencies radiated from the directive antennae, means for applying said sideband frequencies to the deflecting members of an indicating instrument, means for obtaining the sideband frequencies from the omni-directional antenna, means for deriving from these last mentioned side band frequencies the same sideband frequencies as those from the directive antennae and for applying the derived sideband frequencies to the deflected member of the indicator.

3. A radio beacon comprising means for modulating a carrier wave of frequency F by two low frequencies f1 and fz an omni-directional antenna system for radiating the modulated carrier frequency, means for applying the two frequencies f1, ,f2 to a detector thereby producing at the output thereof two resulting frequencies (f1-H2) and (fi-J2) means for applying said frequencies (f1-H2) and (f1-f2) separately to modulate carrier frequency F, means for radiating the side.- bands thus produced from two directive antenna systems, whose directive axes are angularly related to each other, means at a receiver for receiving the radiated waves on a single antenna, means for amplifying and detectingthe received waves, means for separating out the frequencies f1 and fz from the detected products and for applying said frequencies f1, f2 to a modulator to derive frequencies (fnl-f2) and (f1-f2) means for applying the derived frequencies (fi-l-fz) and (f1-f2) respectively to the deflecting members of an indicating instrument, means for separating the frequencies (f1-fz) and (h4-f2) from the output of said detected products and means for applying these latter frequencies (fi-fz) and (fi-l-fz) to the deflected member of said indicating instrument.

4. A radio beacon as claimed in claim 3 in which at the receiver the derived frequencies (f1-H2) and (fi-fm are applied together to the deflected member of an indicating instrument and the frequencies (fi-l-fz) and (f1-fz) obtained directly from the detected received Waves are applied separately to the deflecting members of said indicating instrument,

5. A radio beacon system comprising means for modulating a carrier Wave frequency F by two low frequencies f1, f2 an omni-directional antenna system for radiating the modulated frequency F, a detector to which the frequencies f1, f2 are applied to produce one of the sum and difference frequency products (f1-f2), (fi-l-fz) from the output thereof, means for modulating carrier frequency F with a portion of the output of said detector, and for radiating the resulting modulated carrier from one of two angularly related direc- Vtive systems, a phase shifter to which another portion from the output of said detector is applied to shift the phase thereof means for applying the phase shifted frequency to modulate carrier frequency F and means for radiating the resulting modulated frequency from the other of said two angularly related systems, and at a receiver a single antenna for receiving said radiated waves, means for amplifying and detecting said waves to obtain therefrom the said one of the sum and difference products (f1-f2), (fi-l-z) means for applying said one frequency to one member of a phase difference indicator, means for separating the frequencies f1 and f2 out from 7 fthe'f-detecte'd1fproductsvof the nreceiver, :a )modulator towhich Vthese yfrequencies ffrand fzare iapplied, means for obtaining: the said one frequency ffromtheoutput of Asaid modulator and for applying gthe said-one frequency-so obtained to the fothermember ofsaid phase `difference indicator.

6. A radio beacon system comprising means formodulating a carrierfrequency Fby two low -frequenciesrfi and f2, an omni-directional an- -tenna system forradiating the modulatedcarrier frequency,.directive antenna systems for radiat- Eing the frequencies 2(11-12) and `2(fi+f2) respectively, asingle vantenna on a mobile receiver for receiving said radiated frequencies, means for amplifying and detecting the received Waves, -means for :separating out the frequencies f1 and f2 from the detectedproducts and for 'applying said ,frequencies Afrand fato amodulator to produce frequencies (f1-H2) .andifi-fzhmeans for dourbling Said frequencies (f1-H2) and (f1-f2) to produce the frequencies 2(f1-l-fz') and 20H-f2), :and meansfcr applying these doubled frequencies to-the deectedmember of van indicating instrument, means kfor separating frequencies2(f1+f2) andeZUi-fa) outfrom the said detected products and for applying them respectively tothe delect -ing 'members of said indicating instrument.

7. AA radiobeacon system as `claimed in claim'l .comprisingat a receiver an indicating instrument :havingdeflecting members and. a deflectedmemaber,v means for obtaining the sideband frequencies radiated-from thedirective antennae, means-for :applying said sideband frequencies to either said :deflecting members or said deected member, 'means for obtaining the sideband frequencies ffrom the omniedirectional antenna, means for gderivingfrom these last-mentioned sideband fre- :quencies the. same sideband frequencies as'those Kfr omfthe directiveyantennae, and means for ap- ;.plying said derived sideband frequencies to whichever-of said deiiecting members or deflected member said rst mentioned sideband frequencies .have not been applied.

1,8. Aradio' beacon system for obtaining directly on a mobile receiver the angular position (bear- :ing-or direction) with respect to the transmitting station comprising means for radiating omni-di- ;rectionally a` carrier frequency F modulated with vfrequencies f1 and f2 means forra'diatingtwo directive beams angularly relatedto each other of -said carrier F angularly related to each other and modulated by two auxiliary frequencies de- :rived from f1 and fz, and at the receiver means for obtaining from said, auxiliary frequencies the two .frequencies f1 andgfaand means for utilizing the fobtained frequencies for comparison with the corresponding received frequencies f1, f2 from the omni-directionally transmitted beam.

y9. -A'radio beacon system for obtaining directly fon amobile receiver the angular position with .respect to the transmitting station comprising tmeans `to generate a Vsingle-radio frequency carrier wave,.means toggenerate a plurality of low frequency Waves, means to modulate a single radiofrequency carrier wave by-a plurality' of low frequency waves, meansfor radiating omni-diyrectionally at least ,one of thesidebandscorrespondingto,twoof these Waves, means for modulatine the carrierfrequency with two other low frequency waves, -an angularlyrelated aerial sysstem, forradiatingatleast two beams, and means connecting one. modulator of theother low frel quency waves to Vone directive aerial and the other modulator to another directive. aerial for fradiatinggfrom each cfptlieransularly related 'difrequency with one :of the means and-from-thel modulatory lof .the otheraux- -(bearing or direction) 10.,A vradio beacon system r.for .obtaining fdi- -r'rectly on a-mobile receiverztheangular position (bearing orv direction) vWithyrespect to aztransmitting station comprising an omni-directional radiating means, means to generate a carrierfrequencyRimeans to generate frequenciesji and f2, means tomodulate ,the carrier frequencywith frequencies frand f2, :means for .radiating'two directive beams angularly related to each; other, means deriving vtwo auxiliary frequencies `from frequencies, f1 and jameans modulating said carrier frequency .F by eachof the twoauxiliary frequencies derived from frequencies 'f1 Vand "fz, connections from one modulator of an auxiliary :directive :radiating iliary frequency to the other directive radiating meanaand atthe receiver, means for obtaining said auxiliary Vfrequencies from the s two vreceived frequencies ifi and fafand means for utllizinggthe obtained frequencies vfor `comparison with the corresponding received auxiliary frequencies lfrom the directionally transmitted beam.

1l. .Aradidbeacon system forobtainingvdirectly on a mobile receiver vtheangular position (bearingor direction) 'with respect to the transmitting station comprising an omni-.directional radiating means, means to generateacarrier frequency F, means'to generateffrequencies f1 and f2, means'to modulate the vcarrier frequency'with frequencies f1 and f2, meansfor radiating two directive beams angularly related to each other, means generating two auxiliary frequencies derived from frequencies f1 and f2 means modulating said. carrier frequency F by-each of the two auxiliary frequenciesderived from .frequencies 'f1 and fz, connections from one modulator of an `auxiliary lfrequency with one of the directive -radiating means and from the .modulator ofthe other auxiliary frequency to the other directive radiating means.

.112. A radio beacon system for obtaining directlyv on a mobile receiver the angular position (bearing or direction) with respect to the transmittingstation comprising an omni-directional `radiating means, means to lgenerate a carrier Afrequency means to generate frequencies fi and f2, means to modulate the carrier frequency with frequencies f1 -and f2, means for radiating '.t-wo directive beams angularly related to each other, means generating two auxiliary waves derived from frequencies f1 and f2 and having a frequency differing therefrom, means modulating said carrier frequency F byeach of the two yauxiliary waves derived from frequencies f1 and f2, connections from one modulator of an `auxiliary wave with one of the directive radiating means and from the other modulator to the other directive radiating means, and at the receiver,

-means for obtainingfrom said auxiliary frequencies the twojfrequencies 'f1 and fz, and means for utilizing the'obtained frequencies for comparison with the rcorresponding received frequencies ji,

and ffzyfrom the omni-directionally transmitted beam.

13. A rradio beacon system for obtaining directly on a mobile receiverthe angular position with respect to the transmitting station comprising an omni-directional `radiating means, means to generate a carrierfrequencyRmeansto generate frequencies f1 and f2,

-means to-modulate the carrier-frequency with frequencies f1 and f2, directive beams;'angularlyY relai-,edl to each ot-her,

-means Ifor radiating -two means generating two auxiliary waves derived from frequencies f1 and f2 and having a frequency differing therefrom, means modulating said carrier frequency F by each of the two auxiliary waves derived from frequencies f1 and f2, and connections from one modulator of an auxiliary wave with one of the directive radiating means and from the other modulator to the other directive radiating means.

14. A radio beacon system for obtaining directly on a mobile receiver the angular position (bearing or direction) with respect to the transmitting station comprising an omni-directional radiating means, means to generate a, carrier frequency F, means to generate at least one modulating frequency, means to modulate the carrier frequency with each modulating frequency, means for radiating two directive beams angularly related to each other, means generating two auxiliary waves derived from the modulating frequency and having a frequency differing therefrom, means modulating said carrierdF by each of the two auxiliary waves, and connections from one modulator of an auxiliary wave with one of the directive radiating means and from the other modulator to the other directive radiating means.

15. A radio beacon system for obtaining directly on a mobile receiver the angular position (bearing or direction) with respect to the transmitting station comprising an omni-directional radiating means, means to generate a carrier frequency F, means to generate at least one modulating frequency, means to modulate the carrier frequency F with each modulating frequency, means for radiating two directive beams angularly related to each other, means generating two auxiliary waves derived from at least one modulating frequency and having a frequency differing from the latter, means modulating said carrier frequency F by each of the two auxiliary waves, connections from one modulator of an auxiliary wave with one of the directive radiating means and from the other modulator of an auxiliary wave to the other directive radiating means, and at the receiver, means for obtaining said auxiliary waves, and means for utilizing the obtained waves for comparison with the received modulating frequency from the omni-directionally transmitted beam.

16. A radio beacon system for obtaining directly on a mobile receiver the angular position (bearing or direction) with respect to the transmitting station comprising an omni-directional radiating means, means to generate a carrier frequency F, means to generate at least one modulating frequency, means to modulate the carrier frequency F with each modulating frequency, means for radiating two directive beams angularly related to each other, means generating two auxiliary waves derived from at least one modulating frequency and having a frequency differing from the latter, means modulating said carrier frequency F by each of the two derived auxiliary waves, connections from one modulator of an auxiliary wave with one of the directive radiating means and from the other modulator of an auxiliary wave to the other directive radiating means.

CHARLES WILLIAM EARP.

REFERENCES crrED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,922,677 Greig et al, Aug. 15, 1933 2,129,004 Greig Sept. 6, 1938 2,252,699 Byrne Aug. 19, 1941 2,253,958 Luck Aug. 26, 1941 1,815,246 Englund July 21, 1931 FOREIGN PATENTS Number Country Date 525,182 Great. Britain Aug. 22, 1940 

